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Subject and UNIT: Electronic Devices and Circuits: Unit IV: Feedback Amplifiers and Oscillators
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Subject and UNIT: Electronic Devices and Circuits: Unit IV: Feedback Amplifiers and Oscillators
Anna university important solved Problems
Quartz Crystal Construction, Advantages
Subject and UNIT: Electronic Devices and Circuits: Unit IV: Feedback Amplifiers and Oscillators
The crystal is a thin slice of Piezo-electric material, such as quartz, tourmaline and rochelle salt, which exhibit a property called Piezo-electric effect. The Piezo electric effect represents the chracteristics that the crystal reacts to any mechanical stress by producing an electric charge. In the reverse effect, an electric field results in mechanical strain.
RC Phase Shift Oscillator, Wien Bridge Oscillator
Subject and UNIT: Electronic Devices and Circuits: Unit IV: Feedback Amplifiers and Oscillators
All the oscillators using tuned LC circuits operates well at high frequencies. At low frequencies, as the inductors and capacitors required for the time circuit would be very bulky. RC oscillators are found to be more suitable. Two important RC oscillators are (i) RC phase shift oscillator and (ii) Wien Bridge Oscillator.
Analysis
Subject and UNIT: Electronic Devices and Circuits: Unit IV: Feedback Amplifiers and Oscillators
Introduction and Details of Colpits Oscillator
Subject and UNIT: Electronic Devices and Circuits: Unit IV: Feedback Amplifiers and Oscillators
Introduction and Details of Hartley Oscillator
Mechanism for Start of Oscillations
Subject and UNIT: Electronic Devices and Circuits: Unit IV: Feedback Amplifiers and Oscillators
The oscillators circuit is set into oscillations by a random variation caused in the base current due to noise component or a small variation in the dc power supply. The noise components ie extremely small random electrical voltages and currents and currents are always present in any conductor, tube or transistor.
Classification
Subject and UNIT: Electronic Devices and Circuits: Unit IV: Feedback Amplifiers and Oscillators
Any circuit which is used to generate a periodic voltage without an ac input signal is called an oscillator. To generate the periodic voltage the circuit is supplied energy from a dc source. If the output voltage is a sinewave function of time, the oscillator is called a "Sinusoidal" or "Harmonic" oscillator. It is basically an amplifier circuit with positive feedback. Thus the amplifier can be defined as a circuit which self generating some waveform such as sine, triangular, square etc. It is also known as a converter, it converts power from dc power supply into ac power.
Subject and UNIT: Electronic Devices and Circuits: Unit IV: Feedback Amplifiers and Oscillators
There are four different combinations i. Voltage - series feedback ii. Voltage - shunt feedback iii. Current-series feedback iv. Current - shunt feedback
Subject and UNIT: Electronic Devices and Circuits: Unit IV: Feedback Amplifiers and Oscillators
The sensitivity is defined as the ratio of percentage change in voltage gain with feedback to the percentage change in voltage gain without feedback.
Basic Concept of Feedback
Subject and UNIT: Electronic Devices and Circuits: Unit IV: Feedback Amplifiers and Oscillators
Harold Black of Western Electric Company invented electronic feedback concept in 1928. When he was working on repeaters for telephone lines. Feedback plays a very important role in electronic circuits and the basic parameters such as input impedance, output impedance, current or voltage gain and bandwidth may be altered considerably by the use of feedback for a given amplifier.
Subject and UNIT: Electronic Devices and Circuits: Unit III: Multistage Amplifiers and Differential Amplifier
Anna university Important Two marks Questions with Answers on Multistage Amplifiers and Differential Amplifier